Bug report: Mac Target Disk Mode not working in some cases

[Andrew F. <and...@gm...>]

Hello,

I firstly wanted to thank the maintainers for working on the ieee1394
system for Linux. It's great to see continuing support for firewire in
Linux.

I have encountered a bug in that some Macs are not detected in Linux, when
the Mac is being used in "Target Disk Mode". For those unfamiliar, Target
Disk Mode boots an older (firewire-compatible) Mac in a mode where
connecting it to another computer via firewire causes the Mac to appear as
an external firewire hard drive. See the Wikipedia article
<https://en.wikipedia.org/wiki/Target_Disk_Mode> for more information. To
be clear, I am not trying to run the Linux1394 system on an older Mac; I am
trying to connect a Mac in Target Disk Mode to a regular PC running Linux
over firewire. The Mac should appear as an external firewire hard drive. On
some Mac models, it works just fine. However on other models, it doesn't
work. If I connect one of these non-working models to a Mac running OS X,
it does work, so it does appear to be an issue with Linux1394.

Mac models that work:
Macbook Pro late 2008
iMac G4

Mac models that do not work:
iBook G4
Powerbook G4

I have access to more Mac models to test if necessary - the benefits of
hoarding old electronics!

If the maintainers are interested in investigating this issue, what sort of
debugging information can I provide? There's only a few lines in dmesg that
to my eyes look useful ("sbp_scsi_abort" is one) but I can provide full
dmesg output if helpful. I have a number of different Firewire PCI / PCIe
cards I can use, including one that should be able to run the "nosy"
ieee1394 packet sniffer (although I have no clue how to set that up!).

Many thanks, and kind regards,
Andrew